(a) Technical Field
The present invention relates to a relative humidity and condensed water estimator for a fuel cell, and a method for controlling condensed water drain using the same. More particularly, it relates to an estimator for dynamically estimating relative humidity and condensed water in a fuel cell system, and a method for controlling condensed water drain in an anode of a fuel cell stack using the same.
(b) Background Art
Theoretically, a fuel cell system is a simple system that receives hydrogen and air from the outside to generate electricity and water in a stack. In reality, however, water that is a by-product of electrochemical reactions is changed into a combination of water vapor, saturated liquid, and ice according to the real-time operation conditions such as temperature and pressure. Since these phase changes affect the transfer characteristics of water, and also the transfer characteristics of gases and electrons passing through a gas diffusion layer, a catalyst layer, a membrane, and a separator channel of a stack, it is hard to estimate internal phenomena of the fuel cell system.
Particularly, since the fuel cell system is a system having high non-linearity in which the performance of a stack changes due to coexistence of, so-called, flooding and dry-out phenomena that signify overflow and deficiency of water, respectively, it is more difficult to estimate the internal phenomena of the fuel cell system.
For this reason, a sensor for measuring the relative humidity in the fuel cell system and a condensed water level sensor for sensing the level of condensed water are installed to manage water in the stack. However, when the relative humidity sensor is used, the cost of materials increases. Also, since the relative humidity sensor and the condensed water level sensor easily break down due to frequent contact with water, the maintenance costs may increase, and the reliability may be reduced in terms of control.
Accordingly, there is a need for the development of a technique for determining the relative humidity and the state of condensed water to manage water in a fuel cell system so as to overcome the above limitations.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.